In recent years, a new class of sonic materials has been discovered, based on the principle of structured local oscillators. Such materials can break the mass density law of sound attenuation, which states that in order to attenuate sound transmission to the same degree, the thickness, or mass per unit area, of the solid panel has to vary inversely with the sound frequency. Thus with the conventional sound attenuation materials low frequency sound attenuation can require very thick solid panels, or panels made with very high density material, such as lead.
The basic principles underlying this new class of materials, denoted as locally resonant sonic materials (LRSM) have been published in Science, vol. 289, p. 1641-1828 (2000), and such materials are also described in U.S. Pat. No. 6,576,333, and U.S. patent application Ser. No. 09/964,529 on the various designs for the implementation of this type of LRSM. However, current designs still suffer from the fact that the breaking of the mass density law is only confined to a narrow frequency range. Thus in applications requiring sound attenuation over a broad frequency range the LRSM can still be fairly thick and heavy.